Adds listCommands endpoint to a2a server (#12604)

Co-authored-by: Juanda <jdgarrido@google.com>
Co-authored-by: Shreya Keshive <shreyakeshive@google.com>

packages/a2a-server/src/commands/extensions.ts

@@ -0,0 +1,37 @@
+/**
+ * @license
+ * Copyright 2025 Google LLC
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+import { listExtensions, type Config } from '@google/gemini-cli-core';
+import type { Command, CommandExecutionResponse } from './types.js';
+
+export class ExtensionsCommand implements Command {
+  readonly name = 'extensions';
+  readonly description = 'Manage extensions.';
+  readonly subCommands = [new ListExtensionsCommand()];
+  readonly topLevel = true;
+
+  async execute(
+    config: Config,
+    _: string[],
+  ): Promise<CommandExecutionResponse> {
+    return new ListExtensionsCommand().execute(config, _);
+  }
+}
+
+export class ListExtensionsCommand implements Command {
+  readonly name = 'extensions list';
+  readonly description = 'Lists all installed extensions.';
+
+  async execute(
+    config: Config,
+    _: string[],
+  ): Promise<CommandExecutionResponse> {
+    const extensions = listExtensions(config);
+    const data = extensions.length ? extensions : 'No extensions installed.';
+
+    return { name: this.name, data };
+  }
+}